Laser beam systems for indicating grades are employed in various surveying and construction applications. The laser beam emitted by the grade indicating device can be used as an elevational reference over a work area such as for example a construction site.
If the laser beam emitter of the grade indicating device is arranged to rotate the laser beam in a plane, the rotating laser beam can be used to establish a reference plane as an elevational reference over a two-dimensional work area. Laser beam detectors placed remote from the grade indicating device intercept the laser beam for guidance. The laser beam detectors may for example be mounted on tools or machinery and guide an operator on a construction site or to shape a terrain. For example the laser beam detectors are carried by earth moving equipment to determine proper elevation at various points throughout the work area.
If the laser beam or the reference plane is tilted by a known grade angle or angles for example to a horizontal direction or level plane, the grade indicating device can be used to indicate by way of the laser and thus shape various kinds of slopes, or to match or shape existing landscapes.
It is conceivable that for exact grade indication over long distances it is required to finely adjust the laser beam with regard to a reference direction or reference plane. Usually, if a grade is to be indicated on the basis of a level plane or a horizontal direction of the laser beam, the grade indicating device may be adjusted based on an initial position with the laser beam exactly horizontal or the reference plane in a rotating laser beam application being exactly level. Starting therefrom the grade angle is adjusted to the desired value such as by using stepper motors and a known relation between individual steps of the motor and grade angles. Alternatively the grade angle of the laser may be directly indicated by making use of a sensor affixed to the laser emitter, the sensor measuring an inclination of the laser emitter.
While this approach works well in simpler or small scale applications, many applications require an accuracy that cannot be achieved by the above procedure. For example, the grade indicating device may not be placed in a proper initial position for a level reference plane, temperature variations over time may change once adjusted angles, or the accuracy of the sensor may not be sufficient. These influences lead to potentially large errors of the indicated grade, particularly in larger distances.